1. Field of the Invention
The present invention relates to a backlight unit, and more particularly, to a backlight unit to minimize the area of an inverter PCB and to decrease the number of connectors and power sources required for the backlight unit.
2. Discussion of the Related Art
A cathode ray tube (CRT), a type of flat display device, has been widely used in various applications, including television monitors, measuring machines, and information terminals. However, CRTs cannot satisfy demands for miniaturization and weight requirements due to their large size and relatively high weight. Therefore, various types of alternative technologies have been successfully used as substitutes for CRTs including: liquid crystal displays (LCD), which use an electric field optical effect, plasma display panels (PDP) which use gas discharge, and electroluminescence display devices (ELD), which use an electric field luminous effect.
Among the various display devices, LCD devices have been most actively studied and developed because of their advantageous characteristics such as compact size, low weight, and low power consumption. LCDs have been used in many applications that require ultra-thin flat display devices, for example, monitors for spacecraft, aircraft, notebook computers, laptop computers, desktop computers and other types of large display devices. Because of these various applications, the demand for the LCD devices is continuously increasing.
Most LCD devices operate by controlling the light transmittance from an ambient light source to the display image. Accordingly, it is necessary to provide a light source such as a backlight unit in an LCD panel. In general, the backlight unit used in LCD devices has a cylindrical light-emitting lamp, which is classified into two types according to the arrangement of the light-emitting lamps, either a direct type backlight unit or an edge type backlight unit.
In edge type backlight units, a lamp unit is provided at one side of a light-guiding plate, with the lamp unit being provided with a lamp that emits light. Additionally, a lamp holder is inserted into both ends of the lamp to protect the lamp, and a reflective sheet is provided with one side of the sheet inserted into the light-guiding plate and surrounding the circumference of the lamp. The sheet reflects the light emitted from the lamp toward the light-guiding plate. Because of this structure7 edge type backlight units are generally used in relatively small sized LCD devices such as monitors for laptop computers and desktop computers. Edge type backlight units are advantageous in these applications because they allow the LCD unit to feature a great uniformity of light, a long life span, and a thin profile.
With trends toward using larger sized LCD devices of 20-inches or more, the direct type backlight unit is being actively developed. Direct type backlight units include a plurality of lamps that are formed in parallel on a lower surface of a light-diffusion sheet, whereby an entire surface of the LCD panel is directly illuminated with the light. The direct type backlight unit has greater light efficiency as compared with the edge type backlight unit, and is therefore often used with large-sized LCD devices that require high luminance. For example, direct type backlight units are often used for large-sized monitors or televisions. These units are often operated for extended periods of time and often have long service lives, which often causes lamps to burn out or otherwise become inoperable.
The loss of one lamp in an edge type backlight unit only causes a slight decrease in luminance on the LCD screen. As discussed above, direct type LCD devices are provided with a plurality of lamps directly under the screen of the LCD panel. Accordingly, if one of the lamps burns out or becomes inoperable, the portion of the LCD screen corresponding to the lost lamp is darker than the surrounding portions of the screen.
The edge and direct type LCD devices may use any of the following types of light sources: Electro Luminescence (EL), Light Emitting Diode (LED), Cold Cathode Fluorescent Lamp (CCFL), Hot Cathode Fluorescent Lamp (HCFL) or External Electrode Light-emitting Lamp (EEFL).
Hereinafter, a related art direct type backlight unit using a CCFL will be described with reference to the accompanying drawings, although backlight units with the other types of light sources are equally applicable within the scope of the embodiments.
FIG. 1 is a perspective view of a direct type backlight unit using a CCFL according to the related art. FIG. 2 is a schematic view of showing power supplying wires connected with a light-emitting lamp and a connector of FIG. 1.
As shown in FIG. 1, a related art direct type backlight unit includes a plurality of light-emitting lamps 1, an outer case 3, and a light-scattering means 5a, 5b and 5c. The outer case 3 fixes and supports the plurality of light-emitting lamps 1, and the light-scattering means 5a, 5b and 5c is provided between the light-emitting lamps 1 and an LCD panel (not shown).
The light-scattering means 5a, 5b and 5c is formed of multiple diffusion sheets and one diffusion plate and prevents the silhouette of the light-emitting lamps 1 from being shown on a display surface of the LCD panel (not shown). This structure and orientation provides a light source with uniform luminance. Also, a reflective sheet 7 is provided inside the outer case 3 for concentrating the light emitted from the light-emitting lamps 1 to the display part of the LCD panel, which improves the efficiency of the unit.
In the preferred embodiments, each light-emitting lamp 1 is formed from a Cold Cathode Fluorescent Lamp (CCFL). Also, electrodes 2 and 2a are provided at each end of each CCFL, and the CCFL emits light when electrical power is provided to the electrodes. The ends of each of the light-emitting lamps 1 are fixed to the sides of the outer case 3. Power supplying wires 9 and 9a are connected to the electrodes 2 and 2a that are provided at the ends of each of the light-emitting lamps 1 to transmit power to the light-emitting lamps 1. The power supplying wires 9 and 9a are connected to a driving circuit by an additional connector. Each light-emitting lamp 1 requires an individual connector. As shown in FIG. 2, the power supplying wire 9 connected to one electrode 2 of the fluorescent lamp and the power supplying wire 9a connected to the other electrode 2a of the fluorescent lamp are together connected to one connector 11. The power supplying wires 9 and 9a are curved around the lower side of the outer case 3, and then connected to the connector 11.
In the related art backlight unit for the LCD device, the connector is connected with the power supplying wire of the light-emitting lamp, which is connected to the driving circuit. As discussed above, each of the light-emitting lamps requires an individual connector. Accordingly, the wiring of the related art backlight unit is very complicated. Moreover, the efficiency of the unit is lowered because the power supplying wires are curved and then are connected with the connector in order to decrease the thickness of the backlight unit. Therefore, it is necessary to perform many additional steps to wire the unit, which lowers the manufacturing efficiency and the yield due to the increased number of manufacturing steps.
Additionally, connecting the electrodes with the connector requires the formation of two holes for each lamp that pass through the outer case, and then the insertion of both electrodes of the light-emitting lamp into and through the holes. Accordingly, these steps lower the manufacturing efficiency and make maintenance and repair of the light-emitting lamp more difficult and costly.
Hereinafter, a related art backlight unit will be described with reference to the accompanied drawings.
FIG. 3 is a schematic view of the rear of a backlight unit with a CCFL according to the related art. FIG. 4 is an expanded plane view showing the inverter of FIG. 3.
As shown in FIGS. 3 and 4, a backlight unit using a CCFL according to the related art includes a plurality of light-emitting lamps (not shown) and first and second inverter PCBs 30 and 40. The plurality of light-emitting lamps are mounted or formed on a lower supporter 20. Then, the first and second inverter PCBs 30 and 40 are respectively provided in the left and right sides of the lower supporter 20 to apply a voltage to electrodes formed at both ends of the light-emitting lamps.
Each of the first and second inverter PCBs 30 and 40 includes a connection unit 31 and a driving unit 32. The connection unit 31 includes a plurality of output connectors 33 to apply voltage to the both ends of each of the light-emitting lamps, while each of the output connectors 33 have a pair of high-voltage capacitors 34a and 34b. Also, the driving unit 32 includes a plurality of transformers 35a, 35b, 35c, and 35d, a power connector 37, and a synchronization cable connector 36. The plurality of transformers 35a, 35b, 35c, and 35d apply a raised voltage to the plurality of high-voltage capacitors 34a and 34b. Also, the power connector 37 applies power to the transformers 35a, 35b, 35c and 35d, and the synchronization cable connector 36 synchronizes the first and second inverter PCBs 30 and 40.
Two light-emitting lamps are connected with each of the output connectors 33 of the connection unit 31. Also, in state of forming the pairs of the high-voltage connectors 34a and 34b, the pairs of high-voltage connectors 34a and 34b are connected with the transformers 33 in parallel.
The light-emitting lamps of the backlight unit using a CCFL are driven by connecting each light-emitting lamp with a transformer. Accordingly, because the number of transformers corresponds to the number of light-emitting lamps, the production cost and the size of the backlight unit increases with the larger size of the LCD model. In order to decrease the size of the backlight unit, high-voltage capacitors 34a and 34b are provided corresponding with the light-emitting lamps, which allows the high-voltage capacitors 34a and 34b to be connected with the transformers 33 in parallel.
However, even though the first and second inverter PCBs 30 and 40 are provided to allow a decrease in the number of transformers 33, the length of the connection unit 31 increases. As a result, an unnecessary portion (shown with the slanted lines in FIG. 4) is formed in the lower and upper parts of the driving unit 32.
As the size of the LCD device increases, the size of the unnecessary PCB portion increases with the addition of more light-emitting lamps and the increase in the length of the connection unit. This additional size of the unnecessary PCB portion in the lower and upper parts increases the production cost and the size of the backlight unit.